I never heard the term Demi-sexuality but it boils down to love before sex.
In my experience, this approach can lead to unconscious mind dynamics, where the unconscious firmware of the man and woman will cross program each other, leading to entangled firmware. Marriage used to occur first, before these dynamics. One was celibate before marriage, to build the love and trust, before the sex trigger, after the wedding. This process can last a lifetime, and changes with the stages of life; permanent entangled bond.
Sex before love can still trigger the same firmware dynamics, but this path is more likely to add bugs. Some people will have sex and fall in love, marry, and then divorce due to the bugs not allowing the correct entanglement. it is also not uncommon for the firmware to become more active, in one person, more than in the other, so they cannot get a valid entanglement. This can also leave the stronger connection running, for some time, even after they part; unfulfilled love and future baggage.
Developing love first helps the couples coordinate the preliminary processes, so they are on the same page, when things start to get more intense; entangled particles coordinate in time yet in their own space; body.
My best experience was when I was collecting unconscious mind data. The dynamics were trigger due to sex before love but as love grew. I was the source of the bugs, since I was treating this more as a scientist, collecting data, and not allowing myself to fully flow with it.
A few months ago, I wrote about thought dimensionality theory, and this bonding process allows you to experience 3+-D thoughts with a time element.